Systemic sclerosis (Scleroderma, SSc) can be associated with a high morbidity and mortality. The complexity and heterogeneity of the disease mandates a composite response index that will capture different organ involvement and patient-reported outcomes. There is a critical need for an SSc-combined response index (SSc-CRI) to to facilitate drug development and to allow comparison among clinical trials in SSc, as a similar index did in rheumatoid arthritis. We have assembled a group of international experts who have have expertise in clinical trial design and development of response criteria in different arthritides. UCLA Clinical Coordinating Center has successfully coordinated recently concluded NIH-funded SSc clinical trials. We took the first step in the developing an SSc-CRI by conducting a structured Delphi exercise to develop a provisional core set of items for clinical trials. The Delphi exercise identified 11 domains relevant to diffuse SSc clinical trials. Our long-term goals are to improve methodologically sound SSc clinical trials and increase interest in drug development for SSc. This application aims to develop an SSc-CRI to be used as an outcome measure in diffuse SSc clinical trials. Our central hypothesis is that a core set of variables for patients with diffuse SSc can be used to develop a formula for an SSc-CRI with robust test characteristics. Our Specific Aims for the 3-year proposal are: Specific Aim1. Perform a prospective longitudinal observational clinical study in 200 patients with diffuse SSc to define a reliable, valid and responsive set of SSc measures for an SSc-CRI, based on a recently completed Delphi exercise. Specific Aim 2. Employ a prospective, data-driven, consensus building techniques to develop and quantitatively evaluate candidate definitions for an SSc-CRI for diffuse SSc. The research proposed in this application is significant because it is expected to provide a single SSc-CRI for diffuse SSc, thereby providing an impetus for drug development and improved assessment of efficacy of therapeutic agents in clinical trials. Lay Language: We propose to develop a response criteria for clinical trials in diffuse scleroderma, that can facilitate drug development and hopefully, can lead to effective treatments for scleroderma.